She also held talks on the case with interior minister Fawzy Abdilal when he visited London recently — and British diplomats in Tripoli are now following up the formal request.

There is no treaty deal for British police to enter Libya but officials hope to get permission within weeks. The Government believes that after the fall of Colonel Gaddafi’s regime the political will exists to prosecute the killers of Pc Fletcher, 25, shot outside the Libyan embassy in London in 1984.

MPs want the suspects to face trial in Britain, though the authorities in Libya have argued that it should be held there.

Only one alleged killer is believed to be alive. Ex-embassy worker Matouk Mohammed Matouk was reported to have escaped after being captured last year.